The major objective of this project is the elucidation of the mechanism by which 2, 3-diphosphoglycerate (DPG) and related organic phosphates modify ligand binding by hemoglobin. This includes studies on the binding of 2, 3-diphosphoglycerate as a function of conformation of the hemoprotein, location of the binding site of the cofactor molecule and the role of the cofactor in regulating oxygen release from hemoglobin under physiological conditions. All these methods of approach are and will be applied to HbA, the major constituent of normal human red cells, as well as fetal Hb (HbF) and some abnormal hemoglobin variants, such as HbS.